Project Summary: Young men who have sex with men (YMSM) have high rates of alcohol use and HIV infection. High levels of alcohol use among YMSM may contribute to HIV incidence because heavy drinking may be associated with greater frequency of condomless anal sex (CAS). Although pre-exposure prophylaxis (PrEP) has been effective at reducing HIV infection, PrEP uptake remains low, and many who use PrEP are not optimally adherent. Research examining the association between alcohol use and CAS has yielded mixed results, which may be due to previously uninvestigated factors that interact with alcohol use to influence condom use decisions. Those who consume alcohol may be more likely to engage in cognitive biases which involve assumptions about ?safety? of sexual partners based on characteristics that are inaccurate indicators of HIV status (i.e., ?risk heuristics?). Condom use is less likely with sexual partners who are perceived to be physically attractive, healthy, familiar or known well, or trustworthy. Understanding how partner risk heuristics interact with alcohol use to contribute to HIV risk behavior at the event level is essential to develop intervention programs to reduce HIV incidence among YMSM. The proposed study will also investigate associations among alcohol use, partner risk heuristics, and CAS among PrEP-using and non-PrEP using YMSM. The proposed study will build on the infrastructure of a NIMHD-funded R01 daily diary study of PrEP-using YMSM and add a sample of non-PrEP-using HIV-negative YMSM who will be recruited to participate in the daily diary study from a NIDA-funded U01 longitudinal cohort study. The proposal will build upon the applicant?s existing program of research on HIV risk behavior and provide the applicant with postdoctoral training in a field of research in which she does not have experience (i.e., alcohol use). The proposal will also provide the applicant with training in statistical methods for analyzing intensive longitudinal (i.e., daily diary) data and grantsmanship, which are necessary to launch her career as an independent scientist. The applicant will learn how to analyze daily dairy data using multilevel modeling techniques to test the within-persons associations of alcohol use, partner risk heuristics, and their interaction, with HIV risk behavior. In sum, the goals of the proposed study are to: (1) examine associations of partner risk heuristics and alcohol use on sexual risk behavior; and (2) investigate associations between alcohol use, partner risk heuristics, and sexual risk behavior among PrEP- using and non-PrEP-using YMSM. The proposed study represents formative research on the interactive roles of alcohol use and partner risk heuristics in HIV risk behavior at the event level, which is an important first step to develop interventions that aim to reduce both problematic drinking and the use of cognitive biases, such as partner risk heuristics, as barriers to HIV prevention among YMSM. Further, testing these associations among both PrEP-using and non-PrEP-using HIV-negative YMSM is essential in order to tailor HIV prevention interventions specifically to these groups.